CHEM 2341 Chapter 1

Carbon

Carbon atoms can form strong bonds to other carbon atoms to form rings and chains of carbon atoms Carbon atoms can also form strong bonds to elements such as hydrogen, nitrogen, oxygen, and sulfur.

Four Single Bonds

a carbon atom with tetrahedral geometry two bonds in plane with 109 degrees of separation one bond behind the plane using a dashed wedge one bond in front of plane using solid wedge

Double Bond

a carbon atom with trigonal planar geometry bonds are all in plane and separated by 120 degrees

orbital hybridization

a mathematical approach that involves the combining of individual wave functions for s and p orbitals to obtain wave functions for new orbitals

Electronegativity

a measure of the ability of an atom to attract electrons increases as we go across a horizontal row of the periodic table from left to right and as we go up a vertical column

atomic number (Z)

a number equal to the number of protons in its nucleus in an electrically neutral atom, the atomic number also equals the number of electrons surrounding the nucleus

orbital

a region of space where the probability of finding an electron is high

HONC

typical number of electrons the following atoms share to reach a full octet; also reflects number of bonds they like to make in most organic molecules Hydrogen = 1 electron (or bond) Oxygen = 2 electrons (or bonds) Nitrogen = 3 electrons (or bonds) Carbon = 4 electrons (or bonds)

Resonance Structures

not real structures for the actual molecule or ion, only exist on paper do not represent as an equilibrium Hybrid is drawn by combining solid lines and a dashed line to indicate that the bonds are something in between a single bond and a double bond. a solid line indicates that a bond is present in all structures; a dashed line indicates that a bond exists in one or more structures but not all a delta shows a partial charge for where a full charge exists in one or more structures

atomic orbitals

plots of the square of a wave function in 3D these plots generate the familiar shapes of atomic orbitals

Resonance Theory

whenever a molecule or ion can be represented by two or more lewis structures that differ only in the positions of the electrons two things will be true: 1. no resonance structure/contributor is realistic 2. the actual molecule or ion will be better represented by a hybrid (average) of the structures

electrostatic potential map

regions of relatively more negative charge are red, while more positive regions tend toward blue

p orbital

shaped like a dumbbell

pi bond

sideways overlap of p orbitals

sp3

signifies a hybrid orbital with one part s orbital character and three parts p orbital character

s orbitals

spheres 1s is simple sphere 2s is sphere with inner nodal surface

Valence Electrons

the electrons in the valence shell of an atom the number of these electrons is equal to the group number of the atom (eg. carbon is in IVA and has 4; oxygen is in VIA and has 6)

Valence Shell

the outmost shell of an atom the most important shell because this shell is the one that an atom uses in making chemical bonds with other atoms to form compounds

Octet Rule

the tendency for an atom to achieve a configuration where its valence shell contains eight electrons

Carbon-Carbon Single Bond

two carbon atoms that can use one electron pair between them while also bonding hydrogen atoms or other groups to achieve an octet of valence electrons

Bond Line Formula

• each line represents a bond • each bend in a line (terminus) represents a carbon atom, unless another group is shown • No Cs are written, except optionally for CH3 groups at the end of a chain • No Hs are shown for hydrogen atoms, unless needed to give a 3D perspective, which uses dashed/solid wedges • # of H atoms bonded to each C is inferred by assuming that as many H atoms are present as needed to fill the valence shell of the C (unless a charge is indicated) • when an atom other than C or H is present, its element al symbol is written at its terminus • H atoms bonded to atoms other than C (eg O or N) are explicitly written

Volume

Comprised mostly by the electrons of the atom Electron volume is approximately 10,000 that of the nucleus

Mass

Comprised of the protons and neutrons of the atom e- contribution is negligible

Ionic Bond

Formed by the transfer of one or more electrons from one atom to another to create ions an attractive force between oppositely charged ions

Dash Structural Formula

Has lines that show bonding electron pairs and includes elemental symbols for the atoms in a molecule

Salts

Ionic compounds, which form only when atoms of very different electronegativities transfer electrons to become ions. Usually very high melting solids, often above 1000 degrees Celsius, because of their strong internal electrostatic forces

Elements

Made up of atoms

Compound

Made up of elements combined in different proportions

Triple bond

a carbon atom with linear geometry depicted with bonds in plane and separated by 180 degrees

Formal Charge

The number of valence electrons in an isolated atom minus the number of electrons assigned to the atom in the Lewis structure FC = # of valence electrons - 1/2 # of shared electrons - number of unshared electrons or F = Z - (1/2)S - U where F = formal charge Z = group number of element S = # of shared electrons U = number of unshared electrons sum of all formal charges in a molecule will equal overall charge on the molecule

Isotopes

atoms of the same element (those having the same number of protons) but with different numbers of neutrons, and as a result, different masses these atoms have the same atomic number, but different mass numbers.

Ions

charged particles formed when atoms gain or lose electrons form because atoms can achieve the electronic configuration of a noble gas by gaining or losing electrons

Molecules

composed of atoms joined exclusively or predominantly by covalent bonds

Isomers

compounds that have the same molecular formula but different structures

Atom

consists of a dense, positively charged nucleus containing protons and neutrons and a surrounding cloud of electrons

constitutional isomers

different compounds that have the same molecular formula but differ in the sequence in which their atoms are bonded--they have different connectivity usually have different physical properties (melting point, boiling point, and density, etc) and chemical properties (reactivity)

Covalent Bonds

form by sharing of electrons between atoms of similar electronegativities to achieve the configuration of a noble gas

Lewis Structures

formulas that show all of the valence electrons unshared electrons are dots, and in dash structural formulas, bonding electron pairs are shown as lines have several rules: 1. show the connections between atoms in a molecule or ion using only VE of the atoms 2. for main group elements, the number of VE a neutral atom brings to a Lewis structure is the same as its group number in the periodic table 3. if the structure is a negative ion (anion) we add one electron for each negative charge to original count of VE. if structure is positive (cation) we subtract one electron for each positive charge 4. in drawing, we try to give each atom the electron configuration of a noble gas

sigma bond

has circularly symmetrical orbital cross section when viewed along the bond between two atoms all single bonds are of this type the bond formed from the overlap of an sp3 orbital and a 1s orbital is an example

Shells

levels of energy and distance surrounding the nucleus in which electrons exist